Optically addressable spins are a promising platform for quantum information science due to their combination of a long-lived qubit with a spin-optical interface for external qubit control and readout. The ability to chemically synthesize such systems—to generate optically addressable molecular spins—offers a modular qubit architecture which can be transported across different environments and atomistically tailored for targeted applications through bottom-up design and synthesis. Here, we demonstrate how the spin coherence in such optically addressable molecular qubits can be controlled through engineering their host environment. By inserting chromium (IV)-based molecular qubits into a nonisostructural host matrix, we generate noise-insensitive clock transitions, through a transverse zero-field splitting, that are not present when using an isostructural host. This host-matrix engineering leads to spin-coherence times of more than $10\mu \mathrm{s}$ for optically addressable molecular spin qubits in a nuclear and electron-spin-rich environment. We model the dependence of spin coherence on transverse zero-field splitting from first principles and experimentally verify the theoretical predictions with four distinct molecular systems. Finally, we explore how to further enhance optical-spin interfaces in molecular qubits by investigating the key parameters of optical linewidth and spin-lattice relaxation time. Our results demonstrate the ability to test qubit structure-function relationships through a tunable molecular platform and highlight opportunities for using molecular qubits for nanoscale quantum sensing in noisy environments.

中文翻译：

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通过主机矩阵控制增强光学可寻址分子量子比特的自旋相干性

光学可寻址自旋是量子信息科学的一个有前途的平台，因为它们结合了长寿命的量子位和用于外部量子位控制和读出的自旋光学接口。化学合成此类系统的能力——生成可光学寻址的分子spins——提供模块化的量子比特架构，可以在不同的环境中传输，并通过自下而上的设计和合成为目标应用进行原子定制。在这里，我们展示了如何通过设计它们的宿主环境来控制这种光学可寻址分子量子比特中的自旋相干性。通过将基于铬 (IV) 的分子量子位插入非同构宿主矩阵，我们通过横向零场分裂生成对噪声不敏感的时钟转换，这在使用同构宿主时不存在。这种主矩阵工程导致自旋相干时间超过$10\mu \mathrm{s}$用于在富含核和电子自旋的环境中光学寻址的分子自旋量子比特。我们从第一原理模拟自旋相干对横向零场分裂的依赖性，并用四种不同的分子系统通过实验验证了理论预测。最后，我们通过研究光学线宽和自旋晶格弛豫时间的关键参数，探索如何进一步增强分子量子比特中的光学-自旋界面。我们的结果证明了通过可调谐分子平台测试量子比特结构-功能关系的能力，并突出了在嘈杂环境中使用分子量子比特进行纳米级量子传感的机会。